


Be my Baby

by Bitter_Baristas



Category: Undertale (Video Game)
Genre: Age Regression/De-Aging, Alternate Universe - Underswap, Brotherly Love, Family Fluff, Fluff, Fluff and Humor, Underswap Papyrus, Underswap Sans
Language: English
Status: Completed
Published: 2017-06-05
Updated: 2017-06-05
Packaged: 2018-11-09 04:59:46
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,728
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11097408
Author URL: https://archiveofourown.org/users/Bitter_Baristas/pseuds/Bitter_Baristas
Summary: When Sans is accidentally turned into a child, Papyrus gets to be the big brother. He finds he enjoys it.





	Be my Baby

Ring... ring... ring..!

Papyrus groaned, fighting against his crumpled sheets to turn over. The phone continued shrieking downstairs. He stared at the ceiling, sure if he let the phone ring long enough the caller would give up or Sans would answer himself.

It was probably a wrong number or a telemarketer.

What if it was Sans? Hadn't he gone to Alphys' to train this morning? He might need Papyrus to bring him something or pull something from the freezer to defrost. The skeleton untangled himself from his bed and made his way to the kitchen.

The phone hadn't ceased its cries and it occurred to him that whoever it was had to be calling continuously. He snatched the phone from its cradle and held it to his face, now spurred by a sense of urgency.

"Hello?"

Undyne's voice came through frantically. "Papyrus, y-you gotta get over here, somethings happened to Sans--"

She didn't have a chance to finish before the phone hit the floor. Papyrus teleported as quickly as his mind was racing. Sans was hurt, a horrible accident while training with Alphys. Stars, what if he had dusted? His brother was in trouble and he had been napping at home. Gods, if something happened to Sans he'd never forgive himself. Or Alphys.

He blipped into existence on the Captains front lawn, soul racing as he scanned the area for his brother.

"Papyrus!" Undyne ran towards him from the house, eyes watery behind her glasses.

"Undyne!" He grabbed her upper arms, almost shaking the distressed scientist. "Where is Sans?"

"Oh Papyrus, it was an a-a-accident. I-I didn't mean to, oh Papyrus I'm so sorry!"

Papyrus felt his soul go cold. His hands fell limply to his sides and he stood shell-shocked, eye sockets black.

"He's gone?" His brother, the only reason he got up in the afternoon, was dust. Gone forever. "Sans." His knees crashed into the grass, tears streaming down his face. It felt as if his soul had been ripped from his chest.

"I found him!" Alphys' boomed, jogging into view. Papyrus' skull snapped up, taking in the scene so fast he couldn't process it. The yellow monster did not look stricken by anguish, as someone who had lost a dear pupil might. In her hands she held a squirming, blue bundle. She was a few yards away when something round and white popped out of the fabric, followed by arms and legs. The tiny skeleton scrambled to escape the hold on him, dropping hard to the ground. The fall had to be painful for such a small child, but he didn't stop. On his bare feet in a moment the monster began to sprint, veering when he saw that he was heading to Undyne and Papyrus.

"Hey! Get back here!"

Papyrus could only stare, gears clicking in his mind when he saw the grey tee-shirt that hung off the child's frame. He met luminescent eye lights that were shimmering with fear. Yet he found himself unable to move.

Alphys moved to give chase, Sans already having put an impressive distance between them. Undyne got to the skeleton first, plucking him up mid-dash.

"Oh Sans, I'm so sorry!" she wailed, hugging him. He grunted, flailing in her embrace.

"P-please, lady. Let me down, I need to find my brother."

A fresh wave of tears flooded Undyne's face and she turned him to face Papyrus.

"Sans." Papyrus gawked at the tinier version of his brother, standing to see him fully. Sans paused and mirrored his brothers surprise. A grin broke out on his face, impossibly bright.

"Wowie! I've never seen another skeleton monster besides me and Papy."

Distantly Papyrus heard Undyne stuttering explanations and apologies, promising she'd fix this. Fix Sans... who was now a child.

"What happened?" Undyne squeaked, cowering under his seething anger. Sans winced as well and Papyrus exhaled, trying to gather control of his emotions. Sans was alive and, for the most part, unharmed. That's what was important.

"An accident," Alphys had come to stand beside them. "We were taking a water break. Undyne left one of her experiments on the table and Sans mistook it for his drink."

Papyrus glared at the scientist, fingers clenching into fists.

"How could you leave something like that lying around?" She shrunk under his accusation, the two women shocked by the hard edge his tone had taken.

"Excuse me?" They all looked to Sans, who was still trapped in Undyne's arms. "May I please go? I need to find my brother."

"Sans, it's me." the small skeleton looked incredulously at him. "It's me, Papyrus."

The child shook his head, tears rimming his eye sockets. "Please, let me go. I wanna to go."

"Put him down." Papyrus commanded. Undyne did so, hovering behind Sans in case he tried to flee again. "Look at me, Sans, I know I'm a lot bigger but it's me. It's Papy." He knelt, meeting his brothers unsure gaze.

"Mister, my brother is a baby bones."

"Undyne?" Papyrus looked helplessly at the fish woman, rising to stand.

"It appears he had reverted back to the mind and body of a child." She provided, finally calm. "From his appearance I would approximate his age between five and eight."

"How are we going to fix this?"

As they bickered, Sans backed away. Consumed in their argument, no one took notice, allowing him to break into a run.

"What do you mean you don't know how this happened? You left an unfinished, liquid experiment on the table in a glass!" Papyrus stalked closer, Undyne receding with each step he advanced.

"Enough!" Alphys roared. "Sans, can you--Sans?"

"Oh dear," Undyne tembled. "He's gone."

Alphys groaned. "Not again." She gave Papyrus a pointed look. "We need to fan out and find him, everything else can wait."

She was right, and with a grim face he nodded.

"Okay."

Papyrus chose not to call out to Sans, figuring his chances of finding him were better if his brother didn't know he was being pursued.

He couldn't have gotten far with his short legs, but his diminished size meant that he had an abundance of potential hiding places.

Where would a young Sans go? He'd said he was looking for his brother, so where would he begin to search for a baby Papyrus?

Their house.

Papyrus almost teleported, then thought better of it. Sans had to be nearby, headed to the house. The Underground wasn't a dangerous place, but he could slip and hit his head or fall into the river. Fear seized his soul, images of Sans’ tiny body floating prone in the water bombarding him.

No. That wouldn’t happen. They were searching in a grid pattern, and if they didn’t find him soon Alphys would call in the guard. They’d find him safe.

If they didn’t Papyrus didn’t know what he’d do.

He shook his head. Those were bridges he had not yet come to, right now he needed to focus on finding Sans.

The lanky skeleton took a deep breath, head cocking. Ahead he heard it, a soft sniffling and the thud of footsteps on the grass.

He followed the sounds, finding Sans looking lost and scared. His soul ached at the sight and he approached cautiously.

"Sans, are you alright?"

The child sniffled, face drawn into a forlorn expression. "How do you people know my name? Where's my brother?"

Papyrus crouched before his brother, offering a hand.

"I know this is confusing, Sans, but I can prove I'm your brother." Sans looked at his hand skeptically, eyes flicking up to familiar orange ones. He took it hesitantly. Papyrus smiled kindly and stood, keeping a secure hold of his brothers hand. The smaller had to lift his arm above his head to make up for the height distance. Papyrus had half a mind to pick up Sans, but decided against in. He'd been manhandled enough for one day. He also decided against teleporting because it always made Sans sick as an adult, as a child it could only be worse.

"Check my Stats." He said. Sans frowned, but obliged. He gasped, sockets wide.

"P-papy?"

The older, at least for now, smiled. "It's me, Sansy."

Arms wrapped around his legs with enough force to make him stumble.

"Papy what happened? Are you okay? Oh, I was so worried!"

"I'm fine, we're both okay." He knelt and pulled Sans into a hug that was returned with vigor. "Sans, can you tell me how old you are?"

"Seven," he murmured. "I just turned seven. And you should be three."

"Undyne, the fish woman, did this to you by accident. You should be..." Goodness, how old was Sans? "Twenty-six, you'd be twenty-six in September."

"Wow," Sans' eye lights lit up with stars. "I'm old!"

Despite the gravity of the situation, Papyrus smiled. "Heh, yeah. Come on, let's go home. We'll get this all sorted later."

"Okay Papy!" Sans took his hand and lead them to their house, head swiveling every few moments to survey the area. He’d stop occasionally, motioning for Papyrus to stay behind him. It was surreal, Sans watching for danger at every corner and putting himself between Papyrus and the possible threats. It reminded him just how much Sans had done for him, how much he'd been forced to grow up.

When the arrived home, Papyrus opened the door for Sans and they stepped inside, the smaller gasping.

"A lot of time has passed," Papyrus said gently. "I'm sure things are a lot different."

"We have a couch? And a TV! Oh my gosh this is amazing!" The child ran through the living room and into the kitchen, where he threw open the pantry door. "Food!" He cried joyfully. "Look at all the food, Paps!"

Watching Sans' excitement was a double edged sword. He was painfully adorable, but his amazement over food was a harsh reminder of how hard their childhood had been. "I must have gotten a good job, huh?" The question interrupted his thoughts and Papyrus smiled.

"Yeah, you take good care of us."

Sans beamed. “Of course! I’m the Magnificent Sans. What kind of brother would I be if I didn’t take good care of you?” He spread his legs, striking a heroic pose.

A wash of sadness overcame Papyrus. Sans had never stopped looking out for him. Over the years he dialed back the intensity of his protectiveness, but even as an adult Sans made sure his brother was fed and taken care of. And Papyrus had done nothing to return the favor. He could have gone with Sans to train instead of sleeping. Tragedy had been avoided today, but what about everyday previous or in the future? Sans was so small, so precious and trusting. It would be easy for an ill intending monster to harm him.

Papyrus sighed, shaking his head to stop those thoughts. Under normal circumstances Sans was capable of fending for himself, and while he currently was not Papyrus would care for him.

And he’d start with new clothes.

“Let’s get you something that fits. We should have some around here...” Sans was fastidious about cleanliness, but he was also sentimental. Somewhere there had to be a tucked away box filled with clothes from their youth.

This time Papyrus did pick Sans up, his small body fitting perfectly in the crook of his arms. Sans settled comfortably against him as they climbed to the attic.

Papyrus had been right about Sans saving their childhood items. Among seasonal decorations and forgotten things were three large cardboard boxes, each neatly labeled.

“Let’s see what we have here.” He set Sans down and pulled out the box labeled ‘clothes’. Inside were mostly onsies and clothes Papyrus had quickly outgrown. “This… this might fit you.”

Sans ended up dressed in black shorts and a yellow tee-shirt, a big improvement from the shirt that hung off him like a dress.

Papyrus observed his handiwork. “What do you think?”

His brother looked down at himself and gave a toothy grin. “I LOVE it!”

A chuckle bubbled out of his mouth and Papyrus returned the grin.

“Glad to hear it.” The grin fell when he suddenly realizing he had no idea what to do next. Watch television, eat, wait for Undyne to figure out how to reverse this?

Undyne. Crap. “I need to call someone.” he said hurriedly.

He had never dialed so fast in his life, not even to order pizza. “Hi, Undyne, yeah I found him. He’s fine. No, not a thing. Yeah I’ll bring him by tomorrow. Okay, bye.”

Sans had remained glued to his side, small hand holding onto his hoodie. His other hand was at his face, thumb sucked into his mouth. Papyrus didn’t remember much from when he was child, but he knew that Sans only sucked his thumb when he was nervous or stressed. Usually he did it while they were watching horror movies.

He got onto his knees and pried Sans’ thumb out of his mouth. Leaning back on his haunches he observed his brother. Sans had photo albums full of pictures of him, but few of himself. When he was full grown, Sans was about four and a half feet tall. His seven year old self was close to three feet tall, and his smallness only added to his cuteness. Blue eye sockets filled his expressive face and a teal flush tinted his cheeks. It was almost too much for Papyrus’ soul to take.

He truly hoped Undyne could get Sans back to his real age, but in that moment he thought that it wouldn’t be terrible to be the elder brother. To repay all that Sans had done for him when he was a child.

“Papy?”

Sans’ small voice made a lump form in Papyrus’ imaginary throat and he pulled the younger into a hug.

He suddenly wanted to punch Undyne a lot less.

His rational mind reminded him that his situation was, hopefully, temporary. Making the most of it was crucial. Pampering Sans for his years of hard work started now, with dinner.

“Want pancakes?” He asked.

Sans face took on a quizzical expression. “For dinner?”

The elder shrugged, and that was enough reasoning for the Sans.

“Alright, you sit here,” he lifted Sans onto a barstool at the counter. “And I’ll make them.” He set to getting all the ingredients and utensils, maxing out his cooking skills.

“Ooh! Can we mix in sprinkles?”

Papyrus smiled, “I like the way you think.” He poured a generous amount to the batter, the bleeding colors swirling as he stirred.

Sans dug ravenously into his stack of pancakes. “Mft!” He swallowed the mouthful of food. “Can I have something to drink?”

“Yeah,” Papyrus grabbed a glass and filled it with milk. Sans gulped it down quickly, leaving a milk mustache above his mouth.

“You should drink some too, Papy. Milk makes bones grow big and strong.”

“I mustache you a question, how do you think I got so tall? Because you had me drink that stuff when I was a kid.”

Sans blinked, not understanding. Papyrus tried again, “Do you not find that a-moo-sing?”

He laughed that time, eyes closing from the force of it. “P-papy, what do you call milk that gets whatever it wants?”

“What?”

“Spoiled milk!”

Papyrus snorted. “Good one, Sans.”

They finished eating between bad puns and jokes.

“Sans, why didn’t the cannibal eat the clown?”

“Oh! I know this one. He tasted funny!” Sans dissolved into hysterical laughter. Huffing, he sat up. “I learned that one on a nice-cream wrapper.”

After they finished eating Sans was shaking in his seat, legs bouncing and fingers tapping the table.

Papyrus paled. Sugar rush.

. . .

Sans having chocolate as an adult was bad, this was a catastrophe. It had taken an hour long tickle fight and several races around the house to finally get him ready for bed. Tucked in and blue eyes drooping, Papyrus decided to seal the deal and pulled out their favorite storybook. Sitting beside his brother, he read aloud, throwing his voices for all the different characters. By the ending, Sans was almost asleep.

“Okay, goodnight buddy.” He kissed Sans’ forehead and left the hall light on. “I’m just next door if you need me.”

In the morning, when he awoke to Sans nuzzled against him, he concluded that this wasn’t so bad.

**Author's Note:**

> This started with the idea of how elated Sans would be if the same situation turned Papyrus into a baby/toddler. He'd be so happy to be able to baby his bro again :)  
> But I couldn't resist some older brother Papyrus action. This will probably be a two or three chapter fic. Possible a part two, starring baby Papy if I don't get lazy.
> 
> Edit, 2018: Uh, yeah... this is gonna be a really bad one shot because I totally abandoned this fic. For a year. Woops.


End file.
